The present invention relates to an apparatus for shifting change speed gears of a transmission for a four-wheel drive motor vehicle which is also selectively driven by two wheels.
A four-wheel drive vehicle having a set of continuously driving wheels and a set of selectively driving wheels for four-wheel driving is known and a transmission provided with an extra low speed gear or emergency low gear for four-wheel driving is known. The extra low speed gear has a higher reduction gear ratio than the first speed gear and is used when high reduction gear ratio driving is necessary, for example, driving up an extremely steep hill by four-wheel driving. If the vehicle is driven by two wheels in the extra low speed gear, a differential, axles and other components of the two-wheel driving system are subjected to an excessive heavy load. Since such a severe driving condition is done at four-wheel driving, it is not necessary to construct the two-wheel driving system with high strength structure so as to bear the excessively heavy load. However, it is necessary to provide a device for preventing the shifting into the extra low gear during two-wheel driving in order to avoid breakdown of the two-wheel driving system.